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Source: So. Dakota State Univ news release

As temperatures and humidity soar, dairy cattle may start to show signs of heat stress, explained Tracey Erickson, SDSU Extension Dairy Field Specialist.

"Dairy cattle have a comfort zone of between 41 to 68 degrees Fahrenheit. For each degree ambient temperatures increase above 68 Fahrenheit dry matter intakes drop on average 0.17 pounds. ," she said. "Producers need to be vigilant in their heat stress abatement tactics."

Signs of heat stress

Reduction in dry matter intake and increased water intake are indicators of heat stress. In addition, Erickson said producers will see a drop in milk production and butterfat, along with increased reproductive issues such as pregnancy loss.

Other heat stress indicators include: open mouth breathing, increased respiration, sweating, increased amount of time standing, and changes in manure consistency.
So what can you as dairy producers do to help aid in the reduction of heat stress? What follows are some basic tips for dairy cattle heat stress reduction:

Provide shade if cattle have access to an outside lot.

Increase access to clean, fresh drinking water. This may involve adding extra tanks of water and checking for appropriate flow of water in drinking fountains.

Cattle waiting in a holding pen in a milking parlor should be cooled by a combination of air movement, water sprinkling systems, and shade.

Make sure sprinklers dispense large water droplets (soaking) as small droplets often found in misters will not allow for heat dissipation from the cow. Intermittent application allows time for the water to evaporate and cool the animal before the next cycle. Sprinkle cows with low pressure sprinklers over their backs away from the feed bunks. Trying to keep the udders dry in this process will help minimize the incidence of mastitis.

Use large fans in combination with sprinklers to help cool cows and the air simultaneously.

As dry matter intake decreasesadjust diets accordingly, utilizing higher quality forages and increasing the energy density of the diet. As diet adjustments are made care should be taken to make sure that there is enough effective fiber to maximize rumination and keep acidosis and displaced abomasums to a minimum. Adding buffers such as sodium bicarbonate to energy dense diets also help aid in maintaining rumen pH under control.

Diets should contain at least 0.25 lbs. of white salt per cow per day, along with offering access to free choice salt and trace minerals.

"It is well known cow comfort is essential for high milk production especially during periods of heat stress. Taking the time to focus on cow comfort aids such as additional fresh clean water, air movement, shade, evaporative cooling via sprinklers, while providing energy dense, palatable diets will help minimize lost milk production and reduced reproductive efficiency due to heat stress," Erickson said.

Heat Stress and the Diet

Heat is produced as a result of microbial fermentation in the rumen. Low quality, stemmy forages generate more heat of fermentation inside the animal, contributing to the animal's total heat load, explained Alvaro Garcia, SDSU Extension Agriculture & Natural Resource Program Director and Professor of Dairy Science.

"Heat is used to maintain body temperature when ambient temperatures are low (below 40 degrees Fahrenheit). However, when ambient temperatures are high the cow needs to maintain its body temperature within biological limits compatible with life," Garcia said.

He explained that the cow's options are limited. "She can drink more fresh water (water evaporation from the body dissipates heat). She can also look for cool spots like ponds, shade, and places with good air circulation, or she can decrease her dry matter intake," he said.

High quality forages are digested faster and result in less heat being produced. So, Garcia encourages dairy producers to consider enriching the ration whenever feed intake decreases due to heat stress.

Energy of particular concern, he explained, as most of it is derived from the fermentation of forages within the rumen. "Increasing energy density might require greater amounts of concentrate and/or byproducts," he said. "Keep in mind that shifting the grain/forage ratio may increase the risk of not having enough rumen "scratch factor" (effective fiber) to optimize rumination."

When the rumen mat formation is inadequate, saliva production decreases (less chewing activity). This, Garcia explained, decreases rumen pH and allows more grain to be fermented in the abomasum and intestines.

Adequate particle size and the use of buffers such as sodium bicarbonate are critical in these "hot rations" to minimize the risk of digestive disorders such as acidosis and displaced abomasum. "Sweating aids in heat dissipation, and sodium and potassium are secreted in sweat. This is a problem particularly in high producing dairy cows, which eliminate more of these minerals in milk," Garcia said.

When environmental temperatures are above 68 degrees Fahrenheit, make sure that diets contain at least .25 pounds of white salt per cow per day. Plenty of fresh, high quality water should also be available. "Test it," Garcia said. "You don't want water already high in sodium. Alleviating heat stress in dairy cattle is a challenge in every South Dakota summer."

Maintaining optimum nutrient balances and providing highly palatable, digestible feeds and ample supplies of fresh, clean water, along with shade and ventilation, will go far towards keeping dairy cows comfortable and their milk production up.

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